This invention relates to tufting machines and more particularly to a new and improved needle bar shifting apparatus for shifting the individual yarn ends transversely between the longitudinal rows of pile formed by the tufting machine.
The art of tufting incorporates a plurality of yarn carrying spaced needles extending transversely across the machine and reciprocated cyclically to penetrate and insert pile into a backing fabric fed longitudinally beneath the needles. During each penetration of the backing fabric a row of pile is produced transversely across the backing. Successive penetrations result in a longitudinal row of pile produced by each needle. This basic method of tufting limits the aesthetic appearance of tufted carpet so produced.
Both the noticeable alignment of the longitudinal rows or "corn cob effect" and the visible optical streaking resulting from variations in coloration of the yarn that detracts from the appearance of a carpet can be effectively overcome by shifting the needles relatively to the backing fabric. Stepping of the needle bar laterally so that each needle stitches in a zig zag manner is the most popular of the methods of obtaining the relative shifting between the needles and the backing.
Various devices have been proposed and are in use for controllably applying a step-wise force to the needle bar of the tufting machine in accordance with a pattern. For example, the primary means for supplying this jogging has been a pattern cam driven in timed relationship to the reciprocation of the needle bar and acting upon a cam follower mechanism coupled to the needle bar. Exemplary of this prior art device are U.S. Pat. Nos. 3,026,830 and 3,934,524. Because of the generally limited longitudinal pattern repeat of a cam, the cam providing a longitudinal repeat every revolution thereof, other prior art needle bar shifters have been developed. The known systems are disclosed in U.S. Pat. Nos. 3,964,408 and 3,972,295, which utilize pawl and ratchet devices; U.S. Pat. No. 4,010,700 which uses an indexing device; and U.S. Pat. No. 4,173,192 which uses a hydraulic actuator.
In each of the known prior art needle bar shifters a member connected to the needle bar is transversely or laterally moved by the shifter mechanism while the needle bar is in the upper portion of its vertically reciprocating travel and the needles are above the backing fabric. In a fall sized tufting machine a needle bar weighs in order of 100 pounds. Thus, during the needle bar reciprocation a substantial force must be exerted on the moving needle bar to step it laterally within a relatively short period of time. Due to this inertia difficulty tufting machines operating with a needle bar shifter are run at speeds substantially lower than that which they are otherwise capable. This reduction in speed is generally in the order of approximately one-half the speed of machines which run without shifters and the yardage output is decreased proportionately.